1. Technical Field
The present invention relates to a multi-layered capacitor, and more particularly, to a multi-layered capacitor that can noticeably reduce an acoustic noise caused by oscillation by suppressing deformation of the multi-layered capacitor incurred by a reverse piezoelectric effect when the multi-layered capacitor is operated, and a manufacturing method thereof.
2. Description of the Related Art
In general, a multi-layered capacitor, in particular, a multi-layered ceramic capacitor (MLCC) is a chip-type condenser that is mounted on a printed circuit board of a variety of electronic devices, such as a mobile communication terminal, a laptop computer, a desktop computer, and a personal mobile terminal (such as a personal digital assistant (PDA)), and its main function is charging or discharging electricity. The multi-layered capacitor has diverse sizes and a multi-layered pattern according to its use and capacity.
The current technical trend of such a multi-layered ceramic capacitor is towards miniaturization and ultra high capacity, and this can be realized by thin-layered inner electrodes, and thin-layered dielectric layers and a high number of multi-layered dielectric layers.
Hereinafter, a related art multi-layered ceramic capacitor will be explained in detail with reference to FIGS. 1 to 5.
FIG. 1 is a perspective view schematically illustrating a related art multi-layered capacitor, FIG. 2A is a cross sectional view taken along line I-I′ of FIG. 1 and FIG. 2B is a cross sectional view taken along line II-II′ of FIG. 1, FIG. 3 is a perspective view schematically illustrating the multi-layered capacitor of FIG. 1 which is mounted on a substrate, FIGS. 4A and 4B are cross sectional views to schematically explain deformations of the multi-layered capacitor and the substrate which occur when the multi-layered capacitor of FIG. 3 is operated, and FIG. 5 is a graph schematically illustrating an acoustic noise caused by the oscillation of the multi-layered capacitor of FIG. 3.
As shown in FIGS. 1 and 2B, the related art multi-layered capacitor generally includes a capacitor element 10 and external electrodes 20 formed at opposite ends of the capacitor element 10.
The capacitor element 10 includes a plurality of dielectric layers 10a multi-layered therein, and also includes a first inner electrode 11 and a second inner electrode 12 which are alternately formed on neighboring dielectric layers.
The external electrodes 20 include a first external electrode 21 formed at one end portion of an outside surface of the capacitor element 10, and a second external electrode 22 formed at the other end portion of the outside surface of the capacitor element 10. The first external electrode 21 is electrically connected to the first inner electrode 11 and the second external electrode 22 is electrically connected to the second inner electrode 12.
As shown in FIG. 3, the multi-layered capacitor as described above is mounted on a substrate 30, that is, a printed circuit board, of a variety of electronic devices such as a mobile communication terminal, a laptop computer, a desktop computer, and a personal mobile terminal (such as a PDA), and main function is charging or discharging electricity.
The multi-layered capacitor is fixedly mounted by electrically connecting the first external electrode 21 and the second external electrode 22 to the substrate 30 by means of solders 41 and 42.
However, as shown in FIGS. 4A and 4B, the related art multi-layered capacitor, which is manufactured using a ferroelectric substance, may incur deformation such as expanding outwards or contracting inwards between the first external electrode 21 and the second external electrode 22 due to a reverse piezoelectric effect or an electrostriction property, when the multi-layered capacitor is operated under an alternating current (AC) voltage.
Therefore, there is a problem in that oscillation occurs due to the deformation of the multi-layered capacitor and an acoustic noise occurs due to the oscillation.
In other words, if an electric field is applied to the first external electrode 11 and the second external electrode 12 formed in the capacitor element 10, electric potentials of a positive polarity (+) and a negative polarity (−) are alternately applied in an alternating current (AC) and thus a mechanical displacement of the multi-layered capacitor occurs, causing oscillation, which is the cause of an acoustic noise.
Also, if the mechanical displacement of the multi-layered capacitor is transmitted to the substrate 30 through the solders 41 and 42, deformation of the substrate 30 occurs and thus oscillation also occurs in the substrate 30. Therefore, the acoustic noise becomes more serious. In particular, referring to FIG. 5, it can be seen that the acoustic noise reaches its peak when oscillation of the multi-layered capacitor is transmitted to the substrate, and as a result, the substrate generates resonance.